1. Field of the Invention
The present invention relates to an optical component molding apparatus for molding optical components and, more particularly, to an optical component molding apparatus for molding optical components each of which has a small size (an outer diameter of 2 mm to 12 mm) and high precision (surface roughness Ra of 20 nm or less).
2. Description of Related Art
Recently, optical components such as objective lens are formed in a manner of injection molding using a thermoplastic resin (refer to, for example, Patent Documents 1 and 2). Since, by molding optical components using a plastic, products of uniform configuration can be produced quickly, the molding is suitable for mass production thereof. Optical instruments utilizing the plastic lens have a tendency toward miniaturization and higher performance from year to year. Accompanying this, requests for miniaturization and higher precision of the plastic lens are also increasing.
[Patent Document 11 Japanese Published Unexamined Patent Application No. 11 (1999)-42685
[Patent Document 21 Japanese Published Unexamined Patent Application No. 2001-272501
Further, as a technique for mass production of optical components, there has been studied a so-called multi-cavity molding technique for molding a plurality of molded products (molded articles) in a single mold-clamping and resin-injecting operation. A mold used for the multi-cavity molding has a single sprue centrally provided in a fixed mold and a plurality of runners arranged around the sprue. That is, lens transfer sections are symmetrically arranged around the sprues. In this multi-cavity molding technique, how to increase the number of molded products while reducing variations in transferability to each transfer section has a large influence on commercial profit.
However, the above multi-cavity molding of small-sized and high-precise optical components would be problematic in the following points. Good transferability is required for molding such small-sized and high-precise optical components. For this purpose, runners in the multi-cavity molding machine have a large thickness (diameter). In such runners with a larger diameter, however, it takes a long time to solidify resin in each runner. In other words, the cooling time (duration) is determined depending on the time needed for solidifying the resin in each runner. This makes it difficult to shorten a production cycle.
In the injection molding machine, generally, the optical characteristics of the molded optical components are likely influenced largely from processing accuracy of the molds, face shift (misalignment of lens surfaces in a direction perpendicular to an optical axis of the lens) and tilt (angular misalignment of the lens surfaces with respect to the optical axis) resulting from distortion of the molds which may be caused when the molds are brought into pressure contact with or separated away from each others. In the case where the optical components are to be produced, it is necessary to precisely evaluate eccentricity of the molded products and position adjustment of a transfer member. These conditions become more difficult as smaller-sized molded products are to be molded.